Fuels which are normally a vapor at room temperature and atmospheric pressure may be injected into combustion engines in the liquid state from a low temperature storage tank. There are a number of reasons why it is desirable to inject a liquid into the induction system for a combustion engine, including the fact that liquid fuels are much easier to meter accurately and to deliver, and also because liquid fuels have a higher energy density for each injection in comparison to fuels injected in the gas or vapor state. However, combustion engines utilize exothermic reactions which heat the engine and associated components including the fuel supply rail utilized to deliver liquid fuel to injectors for the combustion engine chambers. Further, combustion engines may be operated under conditions wherein the ambient temperature is much greater than room temperature further increasing the likelihood that fuel being delivered through the fuel supply rail will be vaporized prior to injecting into the combustion engine. Still further, the operating conditions and duration of operation of a vehicle may be such that pressure in a supply tank may increase over time and vapor may have to be discharged to the atmosphere to reduce pressure in the storage tank.
Refueling the low temperature fuel tank may be difficult and slow because the refueling adds heat to the tank and the addition of liquid fuel causes the pressure in the tank to increase which makes refueling slower and requiring more energy to accomplish.
Persons skilled in the art continue to work on developing improvements to such fuel supply systems for combustion engines.